$ { {-2} \times \left[\begin{array}{rr}{2} & {4} \\ {4} & {-1} \\ {2} & {-1}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-2}\times{2} & {-2}\times{4} \\ {-2}\times{4} & {-2}\times{-1} \\ {-2}\times{2} & {-2}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-4} & {-8} \\ {-8} & {2} \\ {-4} & {2}\end{array}\right]}$